A state election Sunday in western Germany offers Chancellor Angela Merkel’s conservatives a tough test against their resurgent center-left rivals six months before Merkel seeks a fourth term in a national vote. The election for the state legislature in Saarland, a region of just less than 1 million people on the French border that Merkel’s Christian Democrats have led since 1999, is the first of three regional votes before Germany’s September 24 national vote. Test for Merkel,